Departing Venice

Since you're flying to Spain from Venice, you need to arrive around 6 a.m. at the airport. The simplest combination of place to stay and transit to the airport is to stay near the Fondamente Nove along the northern edge of the main island of Venice. That puts you near the Fondamente Nove stop for the Alilaguna boat to the airport. You would take the Blue Line, and there's only one stop between F.te Nove and the Marco Polo airport. You can catch the 5:39 Alilaguna boat (Blue Line) and arrive at the airport at 6:07. Or you could stay near Piazzale Roma and take a bus to the airport. The buses are more frequent than the Alilaguna line.

I would suggest either the Hotel Santa Lucia near the train station or the Hotel Papadopoli about 800' from the airport bus at the Piazalle Roma. The hotel Santa Lucia is a very reasonable 1-star hotel that has double, triple and quadruple rooms with en suite bathrooms. Here's the link: http://www.hotelslucia.com/rooms.htm. The ACTV No 5 bus departs the Piazzale Roma at 4:40am for the airport. The first ATVO bus departs at 5:00am. The next buses for both are around 5:40am. With the new bridge over Grand Canal, the Hotel Santa Lucia is within walking distance of the Piazalle Roma. It's about a 10-minute walk. Here's a link to the route. It goes right by the train station. http://gyazo.com/cb127a6a7d8a5c1979c5a87b96aeb8a2 It's a bit more distant from St. Marks by vaporetto but its really close to getting you to the airport early. The Hotel Papadopoli is a 4-star hotel that is really adjacent to the Piazzale Roma. Cross a footbridge from the Piazzle and walk 400' and you're there. It is more expensive and I'm not sure they have rooms large enough for four. To answer your question, with four people, you could take a taxi. The fare on the airport buses is now 6-7 Euro so that's about 40Euro for four. The bus will work fine. The ride to the airport takes about 25 minutes. But, 40E should get you most of the way to the airport in a taxi also. Your choice.

Another option if you can afford the splurge is to hire a watertaxi to sweep the four of you out to the airport across the lagoon. I've never done it (too cheap), but many people say it's a wonderful way to arrive/leave Venice. I'm not sure how much they cost. Someone else might weigh in with that info.

thanks everyone, especially the hotel advice.

The problem with the Alilaguna is that the dock at the airport is a short hike to the airport. The bus from Piazzale Roma goes right to the airport door. Plus, the Fondamente Nova is a very dull neighborhood. I agree with the recommendation for the Santa Lucia. It is a very clean and inexpensive hotel. Not the liveliest neighborhood itself but close to the Piazzale Roma and the train station vaporetto stop.